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Microphones and DI boxes
Published in Trev Wilkins, Access All Areas, 2012
Balanced wiring helps to eliminate any external interference and has better signal integrity, particularly over long runs, when compared to unbalanced lines. As it uses two cores plus a screen the signal is carried along the cores and doesn't rely on the screen to pass its signal. If a ‘ground loop’ problem is causing a hum in a balanced line it's possible to remove the screen at one end in order to break the loop. If the line has phantom power running through it you can't do this though.
Components, Emission Reduction Techniques, and Noise Immunity
Published in David A. Weston, Electromagnetic Compatibility, 2017
The balun is a wideband transformer used to transfer energy from a balanced to an unbalanced line. A common application for a balun is in matching a balanced antenna to an unbalanced cable. In this section we use the term balun to describe a special use of a ferrite or metal oxide bead or toroid. The simple case we will discuss is a balun core with two wires passing through its center. When the two wires carry differential currents, the impedance to these currents at all frequencies is effectively zero. Thus, where the differential currents are caused by a signal, neither the signal amplitude nor rise time is affected by the presence of the core. However, common-mode current due to either current induced by an incident electromagnetic field or noise voltage present between the grounds of two systems is reduced by the series impedance of the balun. A differential-input amplifier with common-mode noise rejection is often compromised in its rejection by the conversion of common-mode (C/M) currents to differential-mode (D/M) voltage. For example, when twisted shielded pair cable is used to carry the differential signal, an imbalance in the pair to shield impedance may result in the conversion of C/M noise to D/M noise. When the circuit impedances are sufficiently low, use of a balun will reduce the C/M current and thereby any D/M induced noise. It is imperative that the two wires be threaded through the same hole in the bead when using a multihole bead. When a single hole is used, the differential signal remains unaffected by the presence of the bead up to 1 GHz and above. However, when the two wires are threaded through different holes, signals with repetition rates as low as 1 MHz are degraded by inclusion of the balun. The high-frequency common-mode noise rejection of an amplifier is invariably compromised by capacitive imbalance to ground on input wiring and PCB tracks and by the poor common-mode noise rejection of operational amplifiers at high frequency. Here the addition of a balun over input wiring may cure the problem by a decrease in the C/M current flow. When the input impedance of the differential circuit is too high, the inclusion of two capacitors, matched as closely as possible in value, located after the balun and between each of the inputs and ground may be the solution.
U
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
umbrella cell E T , where E is the set of points and T the set of gray-levels. The umbra of F is the set U (F) = {(h, v) E × T |v F(h) and v = ±}. The behavior of a morphological operator on graylevel functions can be visualized by applying the corresponding operator for sets to the umbras of the gray-level functions. See morphological operator. umbrella cell a cell that covers the same geographical area as a number of micro- or picocells, and is aimed at supplying seamless service to subscribers with high mobility in these areas. unary operation an operation a computer performs that involves only one data element. The complement and increment operations are examples of such an operation while ADD is an example of an operation that requires two data elements. unbalanced line refers to a signal carrying line where one of the conductors is connected to ground. Contrast with balanced line. unbalanced magnetic pull a phenomenon in electric machines arising from the rotor not being symmetrical with respect to the stator or the axis of the rotor and stator not being coincident. Results in a higher pulling force on the side with the smaller airgap, resulting in additional bearing stresses. unbalanced operation in an n-phase system (n > 1), a condition in which the phase voltages (currents) are either (1) not equal-amplitude sinusoids or (2) have phase angles displaced by a value other than that specified for balanced operation. The term "unbalanced" is also used to describe a machine that has unsymmetrical phase windings. See also balanced operation. ^ unbiased estimate an estimate x of x which is not subject to any systematic bias; that is, ^ E [x - x = 0] See expectation, bias. unbiased estimator an estimator whose mean value is equal to the true parameter value. unbundling a feature of utility de-regulation in which services which were formerly bundled together are sold separately to the customer. uncertain dynamical system model a mathematical model of a dynamical system that includes the system's uncertainties or disturbances. A possible tool to model an uncertain system is to use a differential inclusion, x F(t, x). Another example of an uncertain dynamical system model is x = Ax + Bu + h(t, x, u), where the vector function h models the system's uncertainties. See also matching condition and unmatched uncertainty. unconditional branch an instruction that causes a transfer of control to another address without regard to the state of any condition flags. uncontrolled rectifier a rectifier circuit employing switches that do not require control signals to operate them in their "on" or "off" states. underexcited a condition of operating a synchronous machine, in which the current to the DC field winding is insufficient to establish the required magnetic flux in the airgap. As a result, the machine requires reactive power from the AC system. An underexcited synchronous motor operates at a lagging power factor, as it appears as an inductive load to the AC system. An underexcited synchronous generator operates with a leading power factor, since it must deliver power to a leading (capacitive) system.
Analysis and implementation of compact two-section half-wave balun using artificial transmission lines
Published in Electromagnetics, 2019
A balun performs the function of transforming an unbalanced line, such as coaxial cable or microstrip line, to a balanced line. Because of the output balanced amplitude characteristic with its phase difference of 180°, three-port baluns are important wireless circuit components to realize critical circuit functions, such as double-balanced mixers (Hsiao, Meng, and Peng 2017a), frequency multipliers, and push-pull amplifiers (Chen et al., 2018).